1. Technical Field of the Invention
This invention relates to a silent chain that includes a plate arrangement and structure to reduce the level of noise occurring when power is transmitted.
2. Prior Art
Conventionally, a silent chain, which has been widely used for transmitting power between a crankshaft and a camshaft of an automobile engine, is composed of a large number of link plates on which crotched link teeth are formed for engagement with sprocket teeth. An outer engagement surface or an inner engagement surface of the crotched link tooth contacts the sprocket tooth to effect power transmission.
Various kinds of improvement have been made in such silent chains to reduce the level of noise occurring during power transmission. For example, the silent chain disclosed in Japanese Utility Model Publication No. 6-13399, which is also shown in FIG. 9, adopts a link plate 1 whose inner engagement surface 1a is expanded at the center in a convex shape, and an inner engagement surface 1a of the link plate 1 that begins to engage with the sprocket tooth and another inner engagement surface 1a of the link plate 1 that engages with the sprocket tooth ahead of the former engagement surface 1a are made to contact adjacent sprocket teeth (s1, s2) of the sprocket simultaneously. Thus, the chain is devised so that noise occurring during engagement of the teeth is dispersed to the adjacent sprocket teeth (s1, s2) of the sprocket, and reduced.
However, in the silent chain described in the foregoing Japanese Utility Model Publication No. 6-13399, silent chain tension during power transmission and the tooth shape of the inner engagement surface 1a expanded in a convex shape cause excessive frictional force that interferes with smooth sliding contact between the inner engagement surface 1a of the link plate 1 and the sprocket teeth (s1, s2). Then, the inner engagement surface 1a of the link plate 1 is caught by head portions of the sprocket teeth (s1, s2) to produce contact noise due to the frictional force, and a so-called xe2x80x9crun-uponxe2x80x9d phenomenon, where the link plate 1 runs upon the head portions of the sprocket teeth (s1, s2), occurs as shown in FIG. 9.
The engagement line of the silent chain in which the run-upon phenomenon has occurred is displaced from the sprocket pitch circle L3, to which an ideal engagement line L1 is tangent, by a run-upon width H in the head portion direction of the sprocket tooth in the case where the silent chain smoothly approaches the sprocket S to engage and sit thereon. The run-upon width H is still larger if the inner engagement surfaces 1a of a plurality of the link plates 1 engage with a plurality of corresponding sprocket teeth (s1, s2, and so on) continuously and simultaneously. Accordingly, the traveling line L2 in the free span of the chain floats, causing too much play, such as play in the nature of string vibration, which remarkably amplifies vibration noise.
Therefore, the conventional silent chain having a link plate 1 whose inner engagement surface 1a is expanded at the center in a convex shape has a problem that the contact noise of the inner engagement surface 1a occurring as a result of the foregoing run-upon phenomenon, and the vibration noise of the free span, interfere with the noise dispersion effect resulting from the simultaneous contact of plural inner engagement surfaces 1a, and thus the noise dispersion effect is diminished. Furthermore, there has existed the problem that the run-upon phenomenon produced abnormal elongation and a large load on the link plate 1, shortening the life of the silent chain remarkably.
The object of this invention is to solve the foregoing problems of the prior art, to provide a silent chain capable of reducing the contact noise of the inner engagement surface and the vibration noise of the free span by restricting the run-upon phenomenon and to extend the life of the silent chain life by restricting abnormal elongation and excessive load during power transmission.
A random arrangement type silent chain of the invention is one in which a first link plate, which begins to engage with the sprocket tooth by engagement with an inner crotch, and sits on the sprocket teeth by engagement with its outer flanks, and a second link plate, which engages with and sits on the sprocket teeth only by engagement with its outer flanks, are mixed and combined in the longitudinal direction to form an endless chain. The foregoing problems are solved by setting the mixture ratio of the first link plates to the total link plates to less than 50%, by arranging at least one or more of the second link plates before and after each of the first link plates, and by varying the number of second link plates arranged before and after each first link plate randomly along the length of the chain.
The term xe2x80x9cinner crotchxe2x80x9d as used herein refers to the inner engagement surface of the crotched link teeth formed on the link plate engaging with the sprocket tooth, and the term xe2x80x9couter flankxe2x80x9d refers to the outer engagement surface of the crotched link tooth.
The tooth surface shape of the inner crotch of the first link plate may be a curved shape that swells out a little when superposed on the outer flank (described later) of the second link plate, an arcuate shape or a shape in which these shapes are combined, as long as the tooth surface has a shape in which the tooth can begin engagement with the sprocket tooth by its inner crotch. Further, the tooth surface on the outside may be of a linear shape, a curved shape or a shape in which these shapes are combined, as long as the tooth surface has a shape in which the tooth sits on the sprocket tooth while sliding smoothly and avoiding striking noise.
Further, the tooth surface of the inner crotch of the second link plate may be of a linear shape, a curved shape, an arcuate shape, or a shape in which these shapes are combined, as long as the tooth surface has a shape in which the inner crotch is not allowed to engage with the sprocket tooth, and the outside tooth surface may be of a linear shape, a curved shape or a shape in which these shapes are combined, as long as the tooth surface has a shape in which the tooth sits on the sprocket teeth only by contact with its outer flanks while sliding smoothly and avoiding striking noise.
Moreover, the first link plate and the second link plate, adopted in the random arrangement type silent chain of the invention, may be either a link plate including pin holes for inserting connection pins, or a link plate into which bushings for inserting the connection pins are fitted. Further, the connection pins that combine the link plates into an endless chain may be either round pins having a circular cross-section, or rocker joint type pins in which rolling back surfaces of a rocker pin and a joint pin face with each other.
A sprocket, with which the random arrangement type silent chain of the invention engages, is a regular sprocket including a large number of uniform sprocket teeth, but a sprocket including sprocket teeth whose head portions are dropped out may also be used because it does not cause the run-upon phenomenon.
According to the random arrangement type silent chain of the invention, by setting the mixture ratio of the first link plates to the total link plates to less than 50%, and by randomly arranging at least one or more of the second link plates before and after the first link plates, the inner crotch of the first link plate does not engage with the sprocket teeth continuously and simultaneously even if any link plate in the longitudinal direction engages with the sprocket to cause an engagement pattern due to an arrangement mode of the link plates during power transmission, and thus the conventional run-upon phenomenon is restricted.